Method for carbon nanotube composite structure

ABSTRACT

A method for making a carbon nanotube composite structure is related. A substrate having a first surface is provided. A carbon nanotube structure including a plurality of carbon nanotubes is placed on the first surface, wherein the plurality of carbon nanotubes is in direct contact with the first surface. A monomer solution is coated to the carbon nanotube structure, wherein the monomer solution is formed by dispersing a monomer into an organic solvent. The monomer is polymerized, and then the substrate is removed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 fromChina Patent Application No. 201710365100.8, filed on May 22, 2017, inthe China Intellectual Property Office, the disclosure of which isincorporated herein by reference.

FIELD

The present application relates to a method for making a carbon nanotubecomposite structure.

BACKGROUND

Carbon nanotubes are a novel carbonaceous material having extremelysmall size and extremely large specific surface area. Carbon nanotubeshave interesting and potentially useful electrical and mechanicalproperties, and have been widely used in various fields such asemitters, gas storage and separation, chemical sensors, and highstrength composites.

The composite of carbon nanotubes and polymer can be formed by twomethods. One method includes dispersing the carbon nanotubes into anorganic solvent to form a carbon nanotube dispersion, mixing the carbonnanotube dispersion and a monomer solution, and polymerizing themonomer. However, the carbon nanotubes have poor dispersion in theorganic solvent, which affects the uniformity of the carbon nanotubes inthe carbon nanotube composite structure. Another method includescompletely melting the polymer, and mixing the melted polymer and thecarbon nanotubes. However, the carbon nanotubes have poor dispersion inthe melted polymer because the melted polymer has greater viscosity.Thus, the uniformity of the carbon nanotubes in the carbon nanotubecomposite structure is still poor.

What is needed, therefore, is to provide a method for making a carbonnanotube composite structure that can overcome the above-describedshortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 is a schematic process flow of one embodiment of a method formaking a carbon nanotube composite structure.

FIG. 2 is a scanning electron microscope (SEM) image of a drawn carbonnanotube film.

FIG. 3 is an SEM image of a flocculated carbon nanotube film.

FIG. 4 is an SEM image of a pressed carbon nanotube film including aplurality of carbon nanotubes arranged along a same direction.

FIG. 5 is an SEM image of a pressed carbon nanotube film including aplurality of carbon nanotubes which is arranged along differentdirections.

FIG. 6 is an SEM image of a forth surface of a CNT/PI compositestructure.

FIG. 7 is an SEM image of the forth surface of the CNT/PI compositestructure coated with a gold film.

FIG. 8 is an atomic force microscope (AFM) image of the forth surface ofthe CNT/PI composite structure.

FIG. 9 is an AFM image of the forth surface of the CNT/PI compositestructure coated with a gold film.

FIG. 10 is a schematic process flow of another embodiment of a methodfor making a carbon nanotube composite structure.

FIG. 11 is a schematic process flow of yet another embodiment of amethod for making a carbon nanotube composite structure.

FIG. 12 is a schematic process flow of yet another embodiment of amethod for making a carbon nanotube composite structure.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to illustratedetails and features better. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. For example, substantiallycylindrical means that the object resembles a cylinder, but can have oneor more deviations from a true cylinder. The term “comprising” means“including, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in a so-described combination, group,series and the like.

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, a method for making a carbon nanotube compositestructure 130 of one embodiment includes the following steps:

S1, placing a carbon nanotube structure 110 on a first surface 102 of asubstrate 100, wherein the carbon nanotube structure 110 has a secondsurface 112 and a third surface 114 opposite to the second surface 112,and the third surface 114 is in direct contact with the first surface102;

S2, coating a monomer solution 140 on the carbon nanotube structure 110,wherein the monomer solution 140 is formed by dispersing a certainamount of monomers into an organic solvent;

S3, polymerizing the monomer; and

S4, removing the substrate 100.

In the step S1, the carbon nanotube structure 110 includes a pluralityof carbon nanotubes 118 uniformly distributed therein. A gap 116 isdefined between adjacent carbon nanotubes 118. The plurality of carbonnanotubes 118 is parallel to the second surface 112 and the thirdsurface 114. The plurality of carbon nanotubes 118 is parallel to thefirst surface 102. The plurality of carbon nanotubes 118 can be combinedby van der Waals attractive force. The carbon nanotube structure 110 canbe a substantially pure structure of the carbon nanotubes 118, with fewimpurities. The plurality of carbon nanotubes 118 may be single-walled,double-walled, multi-walled carbon nanotubes, or their combinations. Thecarbon nanotubes 118 which are single-walled have a diameter of about0.5 nanometers (nm) to about 50 nm. The carbon nanotubes 118 which aredouble-walled have a diameter of about 1.0 nm to about 50 nm. The carbonnanotubes 118 which are multi-walled have a diameter of about 1.5 nm toabout 50 nm.

The plurality of carbon nanotubes 118 in the carbon nanotube structure110 can be orderly or disorderly arranged. The term ‘disordered carbonnanotube 118’ refers to the carbon nanotube structure 110 where thecarbon nanotubes 118 are arranged along many different directions, andthe aligning directions of the carbon nanotubes 118 are random. Thenumber of the carbon nanotubes 118 arranged along each differentdirection can be almost the same (e.g. uniformly disordered). The carbonnanotubes 118 can be entangled with each other. The term ‘ordered carbonnanotube 118’ refers to the carbon nanotube structure 110 where thecarbon nanotubes 118 are arranged in a consistently systematic manner,e.g., the carbon nanotubes 118 are arranged approximately along a samedirection and/or have two or more sections within each of which thecarbon nanotubes 118 are arranged approximately along a same direction(different sections can have different directions). The carbon nanotubestructure 110 can be a carbon nanotube layer structure including aplurality of drawn carbon nanotube films, a plurality of flocculatedcarbon nanotube films, or a plurality of pressed carbon nanotube films.

Referring to FIG. 2, the drawn carbon nanotube film includes a pluralityof successive and oriented carbon nanotubes 118 joined end-to-end by vander Waals attractive force therebetween. The carbon nanotubes 118 in thedrawn carbon nanotube film extend along the same direction. The carbonnanotubes are parallel to a surface of the drawn carbon nanotube film.The drawn carbon nanotube film is a free-standing film. The drawn carbonnanotube film can bend to desired shapes without breaking. A film can bedrawn from a carbon nanotube array to form the drawn carbon nanotubefilm.

If the carbon nanotube structure 110 includes at least two stacked drawncarbon nanotube films, adjacent drawn carbon nanotube films can becombined by only the van der Waals attractive force therebetween.Additionally, when the carbon nanotubes 118 in the drawn carbon nanotubefilm are aligned along one preferred orientation, an angle can existbetween the orientations of carbon nanotubes 118 in adjacent drawncarbon nanotube films, whether stacked or adjacent. An angle between thealigned directions of the carbon nanotubes 118 in two adjacent drawncarbon nanotube films can be in a range from about 0 degree to about 90degrees. Stacking the drawn carbon nanotube films will improve themechanical strength of the carbon nanotube structure 110, furtherimproving the mechanical strength of the carbon nanotube compositestructure 130. In one embodiment, the carbon nanotube structure 110includes two layers of the drawn carbon nanotube films, and the anglebetween the aligned directions of the carbon nanotubes 118 in twoadjacent drawn carbon nanotube films is about 90 degrees.

Referring to FIG. 3, the flocculated carbon nanotube film includes aplurality of long, curved, disordered carbon nanotubes 118 entangledwith each other. The flocculated carbon nanotube film can be isotropic.The carbon nanotubes 118 can be substantially uniformly dispersed in theflocculated carbon nanotube film. Adjacent carbon nanotubes 118 areacted upon by van der Waals attractive force to obtain an entangledstructure. Due to the carbon nanotubes 118 in the flocculated carbonnanotube film being entangled with each other, the flocculated carbonnanotube film has excellent durability, and can be fashioned intodesired shapes with a low risk to the integrity of the flocculatedcarbon nanotube film. Further, the flocculated carbon nanotube film is afree-standing film.

Referring to FIGS. 4 and 5, the pressed carbon nanotube film includes aplurality of carbon nanotubes 118. The carbon nanotubes 118 in thepressed carbon nanotube film can be arranged along a same direction, asshown in FIG. 4. The carbon nanotubes 118 in the pressed carbon nanotubefilm can be arranged along different directions, as shown in FIG. 5. Thecarbon nanotubes 118 in the pressed carbon nanotube film can rest uponeach other. An angle between a primary alignment direction of the carbonnanotubes 118 and a surface of the pressed carbon nanotube film is about0 degree to approximately 15 degrees. The greater the pressure applied,the smaller the angle obtained. If the carbon nanotubes 118 in thepressed carbon nanotube film are arranged along different directions,the pressed carbon nanotube film can have properties that are identicalin all directions substantially parallel to the surface of the pressedcarbon nanotube film. Adjacent carbon nanotubes 118 are attracted toeach other and are joined by van der Waals attractive force. Therefore,the pressed carbon nanotube film is easy to bend to desired shapeswithout breaking. Further, the pressed carbon nanotube film is afree-standing film.

The term “free-standing” includes, but not limited to, the drawn carbonnanotube film, the flocculated carbon nanotube film, or the pressedcarbon nanotube film that does not have to be supported by a substrate.For example, the free-standing the drawn carbon nanotube film, theflocculated carbon nanotube film, or the pressed carbon nanotube filmcan sustain the weight of itself when it is hoisted by a portion thereofwithout any significant damage to its structural integrity. So, if thefree-standing the drawn carbon nanotube film, the flocculated carbonnanotube film, or the pressed carbon nanotube film is placed between twoseparate supporters, a portion of the free-standing the drawn carbonnanotube film, the flocculated carbon nanotube film, or the pressedcarbon nanotube film, not in contact with the two supporters, would besuspended between the two supporters and yet maintain film structuralintegrity.

The first surface 102 of the substrate 100 is very smooth. The heightdifference between the highest position of the first surface 102 and thelowest position of the first surface 102 is nanoscale. The heightdifference between the highest position of the substrate surface 102 andthe lowest position of the substrate surface 102 can be defines as asmoothness of the substrate surface 102. The smoothness can also begreater than or equal to 0 nanometers and less than or equal to 30nanometers. The smoothness can be greater than or equal to 0 nanometersand less than or equal to 20 nanometers. The smoothness can be greaterthan or equal to 0 nanometers and less than or equal to 10 nanometers.The material of the substrate 100 should be sapphire, monocrystallinequartz, gallium nitride, gallium arsenide, silicon, graphene, orpolymer. The melting point of the substrate 100 needs to be greater thanthe temperature of polymerizing the monomer. The length, width, andthickness of the substrate 100 are not limited. In one embodiment, thesubstrate 100 is a silicon wafer.

Some organic solvent can be dripped on the second surface 112 of thecarbon nanotube structure 110. When the organic solvent is volatilized,the air between the carbon nanotube structure 110 and the first surface102 can be removed under the surface tension of the organic solvent.Thus, the carbon nanotube structure 110 can be tightly bonded to thefirst surface 102 of the substrate 100. The organic solvent can beethanol, methanol, acetone, dichloroethane, or chloroform.

In the step S2, the monomer can be any monomer that can be polymerizedto form a polymer 120. The polymer 120 includes a phenolic resin (PF),an epoxy resin (EP), a polyurethane (PU), a polystyrene (PS), apolymethylmethacrylate (PMMA), a polycarbonate (PC), polyethyleneterephthalate (PET), phenylcyclobutene (BCB), polycycloolefin orpolyimide (PI), polyvinylidene fluoride (PVDF), and the like. In oneembodiment, the monomer is an imide, and the polymer 120 is a polyimide.The organic solvent includes ethanol, methanol, acetone, dichloroethaneor chloroform.

The monomer solution 140 has a small viscosity and good fluidity. Whenthe monomer solution 140 is coated on the second surface 112 of thesubstrate 100, the monomer solution 140 can pass through the gaps 116and contact with a part of the first surface 102. The first part of thesubstrate 102 is in direct contact with and coated by the monomersolution 140, the second part of the substrate surface 102 is in directcontact with the carbon nanotubes 118. The method for coating themonomer solution 140 is not limited and can be spin coating, injectioncoating, or the like. In one embodiment, the monomer solution 140 iscoated on the carbon nanotube structure 110 by spin coating.

In the step S3, the method for polymerizing the monomer is not limited,such as high temperature treatment. In one embodiment, the substrate 100and the carbon nanotube structure 110 coated with the monomer solution140 are placed in a reaction furnace. The reaction furnace is heated tothe temperature of polymerizing the monomer, and the monomer ispolymerized to form the polymer 120. The part surface of the carbonnanotube 118, that is directly contacted with the first surface 102 ofthe substrate 100, is defined as a contact surface 117. Because thecarbon nanotubes 118 are tubular, the third surface 114 of the carbonnanotube structure 110 is in fact a ups and downs surface. The contactsurface 117 is parts of the third surface 114. Except for the contactsurface 117, the rest of third surface 114 is in direct contact with themonomer solution 140. The gaps 116 are filled with the monomer solution140. When the monomer is polymerized to form the solid polymer 120, thepolymer 120 is combined with the carbon nanotube structure 110 to formthe carbon nanotube composite structure 130.

In the step S4, the method for removing the carbon nanotube compositestructure 130 from the first surface 102 of the substrate 100 is notlimited. The carbon nanotube composite structure 130 can be peeled offfrom the first surface 102 of the substrate 100 by water immersion,blade, tape, or other tools.

The smoothness of the substrate surface 102 is nanoscale, thus thecontact surface 117 can be in direct contact with the substrate surface102 during coating the monomer solution 140 and polymerizing themonomer. Thus, there is no monomer solution 140 between the contactsurface 117 and the first surface 102 during coating the monomersolution 140 and polymerizing the monomer. Thus, when the carbonnanotube composite structure 130 is peeled from the first surface 102,the contact surface 117 is exposed and is not coated by the polymer 120.A part of outer wall of the carbon nanotube 118 directly contacting withthe first surface 102 is exposed and is not covered by the polymer 120.Except for the contact surface 117, the rest of the outer walls ofcarbon nanotubes 118 are coated by and in direct contact with thepolymer 120.

The carbon nanotube composite structure 130 includes the plurality ofcarbon nanotubes 118 and the polymer 120. The plurality of carbonnanotubes 118 are uniformly dispersed in the polymer 120. The pluralityof carbon nanotubes 118 can be joined end-to-end and extend along thesame direction. The plurality of carbon nanotubes 118 can also extendalong different directions, or entangled with each other to form anetwork-like structure. The carbon nanotube composite structure 130 hasa forth surface 132. The forth surface 132 is in direct contact with thefirst surface 102 before peeling the carbon nanotube composite structure130 off from the substrate 100. The length direction of the plurality ofcarbon nanotubes 118 is parallel to the forth surface 132. The surfaceof the polymer 120 near the substrate 100 is defined as a lower surface122. The contact surface 117 and the lower surface 122 together form theforth surface 132. Thus, the contact surface 117 is a part of the forthsurface 132 and exposed from the polymer 120. The contact surface 117 isan exposed surface and can protrude out of the lower surface 122 of thepolymer 120. The height difference between the exposed surface and thelower surface 122 of the polymer 120 is nanoscale. Since the smoothnessof the first surface 102 is at nanoscale level, the forth surface 132 isalso smooth at nanoscale level. The height difference between thecontact surface 117 and the lower surface 122 can be greater than orequal to 0 nanometers and less than or equal to 30 nanometers. Theheight difference between the contact surface 117 and the lower surface122 can be greater than or equal to 0 nanometers and less than or equalto 20 nanometers. The height difference between the contact surface 117and the lower surface 122 can also be greater than or equal to 0nanometers and less than or equal to 10 nanometers.

In one embodiment, the polymer 120 is polyimide, the carbon nanotubestructure 110 is two stacked drawn carbon nanotube films, and the anglebetween the aligned directions of the carbon nanotubes 118 in twoadjacent drawn carbon nanotube films is about 90 degrees.

In one embodiment, to synthesize poly(amic acid) (PAA) solution, 2.0024g of ODA (10 mmol) was placed in a three-neck flask containing 30.68 mLof anhydrous DMAc under nitrogen purge at room temperature. After ODA iscompleted dissolved in DMAc, 2.1812 g of PMDA (10 mmol) is added in oneportion. Thus, the solid content of the solution is about 12%. Themixture is stirred at room temperature under nitrogen purge for 12 h toproduce a PAA solution. The two stacked drawn carbon nanotube films arelocated on a silicon wafer, wherein the angle between the aligneddirections of the carbon nanotubes 118 in two adjacent drawn carbonnanotube films is about 90 degrees. Then the PAA solution is coated onthe two stacked drawn carbon nanotube films, and the PAA solution willgradually penetrate into the two stacked drawn carbon nanotube films toform a preform. The preform is thermal imidized in muffle furnace at 80°C., 120° C., 180° C., 300° C., and 350° C. for 1 h respectively to forma CNT/PI composite structure. Finally, the CNT/PI composite structure ispeeled off from the silicon wafer.

FIG. 6 is an SEM image of the first composite structure surface of aCNT/PI composite structure. As shown in FIG. 6, the carbon nanotubes 118are uniformly dispersed in the CNT/PI composite structure.

FIG. 7 is an SEM image of the first composite structure surface of theCNT/PI composite structure coated with a gold film, and the thickness ofthe gold film is about 1 nm. As shown in FIG. 7, the forth surface 132is a smooth surface with no ups and downs from the naked eye. The heightdifference between the highest position of the forth surface 132 and thelowest position of the forth surface 132 is nanoscale. FIG. 8 is anatomic force microscope (AFM) image of the first composite structuresurface of the CNT/PI composite structure. FIG. 9 is an AFM image of thefirst composite structure surface of the CNT/PI composite structurecoated with a gold film, and the thickness of the gold film is about 3nm. As shown in FIG. 8 and FIG. 9, it is also find that the forthsurface 132 is a smooth surface.

Referring to FIG. 10, a method for making a carbon nanotube compositestructure 160 of another embodiment includes the following steps:

S21, placing the carbon nanotube structure 110 on the first surface 102of the substrate 100, wherein the carbon nanotube structure 110 has thesecond surface 112 and the third surface 114 opposite to the secondsurface 112, and the third surface 114 is in direct contact with thefirst surface 102;

S22, locating a graphene layer 150 on the second surface 112;

S23, coating a monomer solution 140 on the graphene layer 150 and thecarbon nanotube structure 110, wherein the monomer solution 140 isformed by dispersing the monomer into the organic solvent;

S24, polymerizing the monomer; and

S25, removing the substrate 100.

In this embodiment, the method for making the carbon nanotube compositestructure 160 is similar to the method for making the carbon nanotubecomposite structure 130 above except that the graphene layer 150 islocated on the second surface 112 before coating the monomer solution140.

The graphene layer 150 is a two dimensional film structure. If thegraphene layer 150 includes a plurality of graphene films, the pluralityof graphene films can overlap each other to form a large area. Thegraphene film is a one-atom thick planar sheet composed of a pluralityof sp²-bonded carbon atoms. The graphene layer 150 can be afree-standing structure. The term “free-standing structure” means thatthe graphene layer 150 can sustain the weight of itself when it ishoisted by a portion thereof without any significant damage to itsstructural integrity. So, if the graphene layer 150 is placed betweentwo separate supports, a portion of the graphene layer 150 not incontact with the two supports, would be suspended between the twosupports and yet maintain structural integrity. When the plurality ofgraphene films overlap each other, a gap is formed between adjacent twographene films. During coating the monomer solution 140, the monomersolution 140 can pass through the graphene layer 150 and the carbonnanotube structure 110 to arrive at the first surface 102, because boththe graphene layer 150 and the carbon nanotube structure 110 have gaps106.

Referring to FIG. 11, a method for making a carbon nanotube compositestructure 170 of yet another embodiment includes the following steps:

S31, placing the carbon nanotube structure 110 on the first surface 102of the substrate 100 to form a preform structure 172, wherein the carbonnanotube structure 110 has the second surface 112 and the third surface114 opposite to the second surface 112, and the third surface 114 is indirect contact with the first surface 102;

S32, locating two preform structures 172 on a base 174, wherein the twopreform structures 172 are spaced from each other, the substrates 100 ofthe two preform structures 172 and the base 174 form a mold 176 havingan opening, and the carbon nanotube structures 110 of the two preformstructures 172 are opposite to each other and inside of the mold 176;

S33, injecting the monomer solution 140 into the inside of the mold 176from the opening of the mold 176, wherein the monomer solution 140 isformed by dispersing the monomer into the organic solvent;

S34, polymerizing the monomer; and

S35, removing the substrates 100 and the base 174.

In this embodiment, the method for making the carbon nanotube compositestructure 170 is similar to the method for making the carbon nanotubecomposite structure 130 above except the steps S32 and S33.

In the step S32, the method for making the mold 176 is not limited. Forexample, the two preforms structures 172 and the base 174 are fixedtogether by sticking or mechanically fastening to form the mold 176. Inone embodiment, the two preforms structures 172 and the base 174 arefixed by a sealant, and the sealant is 706B vulcanized silicon rubber.The opening is on the top of the mold 176. The carbon nanotube structure110 of each of the two preforms structures 172 is located inside of themold 176. The substrate 100 of each of the two preforms structures 172forms the sidewall of the mold 176. The material of the base 174 is notlimited, such as glass, silica, metal or metal oxide. In one embodiment,the material of the substrate 174 is glass. The carbon nanotubestructure 110 in the mold 176 would not fall off from the substrate 100because the carbon nanotube structure 110 itself has viscosity. Theorganic solvent can be dripped so that the carbon nanotube structure 110is firmly adhered to the substrate 100.

Furthermore, the length or width of the carbon nanotube structure 110can be greater than the length or width of the first surface 102. Whenthe carbon nanotube structure 110 is disposed on the first surface 102,the excess carbon nanotube structure 110 can be folded into the backsurface of the substrate 100, and an adhesive can be applied to the backsurface of the substrate 100. Thus, the carbon nanotube structure 110 inthe mold 176 is firmly adhered to the substrate 100 and would not falloff from the substrate 100. The back surface is opposite to the firstsurface 102, and the first surface 102 can be considered the frontsurface. The melting point of the adhesive needs to be greater than thetemperature of polymerizing the monomer.

In the step S33, the monomer solution 140 is slowly injected into theinside of the mold 176 along the inner wall of the mold 176. The monomersolution 140 completely submerges the carbon nanotube structure 110. Themonomer solution 140 would not break the integrity of the carbonnanotube structure 110 during injecting the monomer solution 140 becausethe carbon nanotube structure 110 is supported by the substrate 100.

Referring to FIG. 12, a method for making a carbon nanotube compositestructure 180 of yet another embodiment includes the following steps:

S41, placing the carbon nanotube structure 110 on the first surface 102of the substrate 100, wherein the carbon nanotube structure 110 has thesecond surface 112 and the third surface 114 opposite to the secondsurface 112, and the third surface 114 is in direct contact with thefirst surface 102;

S42, placing the carbon nanotube structure 110 and the substrate 100into a container 182, wherein the container 182 has an opening;

S43, injecting the monomer solution 140 into the container 182 from theopening of the container 182, wherein the monomer solution 140 is formedby dispersing the monomer into the organic solvent;

S44, polymerizing the monomer; and

S45, removing the substrates 100 and the container 182.

In this embodiment, the method for making the carbon nanotube compositestructure 180 is similar to the method for making the carbon nanotubecomposite structure 130 above except the steps S42 and S43.

In the step S42, the container 182 has a bottom. When the carbonnanotube structure 110 and the substrate 100 are located in thecontainer 182, the substrate 100 is located on and in direct contactwith the bottom of the container 182. The carbon nanotube structure 110is spaced from the bottom by the substrate 100. The material of thecontainer 182 is not limited, such as silica, metal, glass, or metaloxide. In one embodiment, the material of the container 182 is glass.

In the step S43, the monomer solution 140 does not break the integrityof the carbon nanotube structure 110 during injecting the monomersolution 140 because the carbon nanotube structure 110 is supported bythe substrate 100. The amount of the monomer solution 140 can beadjusted so that the monomer solution 140 submerges the entire carbonnanotube structure 110, or submerges only a part of the carbon nanotubestructure 110. When the monomer solution 140 submerges only a part ofthe carbon nanotube structure 110, the thickness of the polymer 120 isless than the thickness of the carbon nanotube structure 110. Thus, inthe carbon nanotube composite structure 180, some carbon nanotubes 118are located in and completely coated by the polymer 120, and some carbonnanotubes 118 are exposed from and extend out of the polymer 120. In oneembodiment, the carbon nanotube structure 110 includes three stackeddrawn carbon nanotube films, and the monomer solution 140 submerges onlya part of the carbon nanotube structure 110. In the carbon nanotubecomposite structure 180, the first drawn carbon nanotube film, thesecond drawn carbon nanotube film and the third drawn carbon nanotubefilm are stacked. The second drawn carbon nanotube film is between thefirst drawn carbon nanotube film and the third drawn carbon nanotubefilm. The entire outer walls of the carbon nanotubes 118 in the seconddrawn carbon nanotube film are coated by the polymer 120. Partial outerwall of the carbon nanotubes 118 in the first drawn carbon nanotube filmare exposed. The contact surfaces 117 of the carbon nanotubes 118 in thethird drawn carbon nanotube film are exposed.

The monomer solution 140 has a smaller viscosity than the moltenpolymer, thus after coating the monomer solution 140 and polymerizingthe monomer, the carbon nanotubes 118 can uniformly dispersed in thepolymer 120. In above methods, the substrate 100 has a nanoscale smoothfirst surface 102, thus some carbon nanotubes of the carbon nanotubecomposites 130, 160, 170, and 180 are exposed from the polymer 120,improving the conductivity of the carbon nanotube composites 130, 160,170, and 180.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Additionally, it is also to be understood that the above description andthe claims drawn to a method may comprise some indication in referenceto certain steps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method for making a carbon nanotube compositestructure, the method comprising: providing a substrate having a firstsurface, wherein the first surface is a nanoscale smooth surface;placing a carbon nanotube structure comprising a plurality of carbonnanotubes on the first surface, wherein the plurality of carbonnanotubes is in direct contact with the first surface; disposing amonomer solution on the carbon nanotube structure to form a compositestructure, wherein the monomer solution is a poly(amic acid) solution,and the poly(amic acid) solution is in direct contact with the pluralityof carbon nanotubes; polymerizing the monomer by heating the compositestructure in a reaction furnace, wherein the plurality of carbonnanotubes is in direct contact with the first surface during disposingthe monomer solution and polymerizing the monomer; and removing thesubstrate.
 2. The method of claim 1, wherein a height difference betweena highest position of the first surface and a lowest position of thefirst surface is greater than or equal to 0 nanometers and less than orequal to 30 nanometers.
 3. The method of claim 1, wherein a material ofthe substrate is sapphire, monocrystalline quartz, gallium nitride,gallium arsenide, or graphene.
 4. The method of claim 1, wherein theplurality of carbon nanotubes is joined end-to-end by van der Waalsattractive force and extends substantially along the same direction. 5.The method of claim 4, wherein the carbon nanotube structure comprisesat least two carbon nanotube films, and an angle between the pluralityof carbon nanotubes in the at least two carbon nanotube films is rangefrom about 0 degree to about 90 degrees.
 6. The method of claim 1,wherein the plurality of carbon nanotubes is substantially parallel tothe first surface.
 7. The method of claim 1, wherein a plurality of gapsis defined by the plurality of carbon nanotubes, and the monomersolution passes through the plurality of gaps and arrive at the firstsurface during disposing the monomer solution.
 8. The method of claim 1,wherein the substrate is a silicon wafer, the monomer is poly(amicacid), and the polymer is polyimide.
 9. The method of claim 1, furthercomprising locating a graphene layer on the carbon nanotube structurebefore disposing the monomer solution.
 10. The method of claim 1,wherein the monomer is polymerized to form a polymer, and some of theplurality of carbon nanotubes are exposed from the polymer afterremoving the substrate.
 11. The method of claim 1, wherein the disposingthe monomer solution comprises placing the carbon nanotube structure andthe substrate in a container and injecting the monomer solution in thecontainer.
 12. The method of claim 1, wherein a method for making thepoly(amic acid) solution comprises: placing 30.68 mL of anhydrous DMAc(N, N dimethylacetamide) in a three-neck flask; placing 2.0024 g of ODA(4, 4′-diaminodiphenyl ether, 10 mmol) in the three-neck flask undernitrogen purge at room temperature; adding 2.1812 g of PMDA(Pyromellitic dianhydride, 10 mmol) in the three-neck flask after ODA isdissolved in DMAc, to form a mixture; and stirring the mixture at roomtemperature under nitrogen purge for 12 hours, to obtain the poly(amicacid) solution.
 13. The method of claim 1, wherein the polymerizing themonomer by heating the composite structure in the reaction furnacecomprises thermal imidizing the composite structure in a muffle furnaceat 80° C. for 1 hour, 120° C. for 1 hour, 180° C. for 1 hour, 300° C.for 1 hour, and 350° C. for 1 hour, respectively.
 14. The method ofclaim 1, further comprising dripping an organic solvent on the carbonnanotube structure, after placing the carbon nanotube structure on thesubstrate and before disposing the monomer solution on the carbonnanotube structure.